In a cellular network, multiple wireless users within a designated area, or cell, communicate with a single base station. In a time division multiple access (TDMA) cellular network, each user communicates with the base station in a time-multiplexed fashion. In other words, each user is allocated a slice of time during which it exchanges a burst of data with the base station wherein a burst is a sequence of digital symbols representing the data. The user must then wait until the other users have exchanged their bursts of data with the base station before exchanging its next burst of data.
The quality of communication in a cellular network can be degraded by a variety of factors. Three important factors are multi-path fading, interference, and noise. These factors can significantly degrade the quality of communication leading to an increase of the bit-error-rate.
One type of multi-path fading occurs when reflections of the transmitted signal arrive at the receiver delayed in time relative to one another. If the relative time delays are a significant portion of a symbol period, then inter-symbol interference (ISI) is produced, wherein the received signal simultaneously contains information from several superimposed symbols.
Another factor that can corrupt the received signal at the receiver is channel interference, in particular co-channel interference (CCI). The increased capacity in a cellular network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be re-used in a different area for a completely different transmission. If there is a single plane transmitter, only one transmission can be used on any given frequency. Unfortunately, there is inevitably some level of interference from the signal from the other cells which use the same frequency. This means that without any measures for suppressing the interference, there must be at least a one cell gap between cells which re-use the same frequency. The frequency re-use factor is the rate at which the same frequency can be used in the network. The frequency re-use factor is given as 1/n where n is a number of cells which can not use the same frequency for transmission. A common value for the frequency re-use factor is 7.
In other words, CCI is the result of receiving the desired signal along with other signals which were transmitted from other radios but occupy the same frequency band as the desired signal. A direct source of CCI is signal energy from other radios operating at the same frequency band as the desired signal. For example, a cellular radio in a distant cell operating at the same frequency can contribute CCI to the received signal in the cell of interest. An indirect source of CCI is adjacent channel interference (ACI) which is the result of side-band signal energy from radios operating at neighbouring frequency bands that leaks into the desired signal frequency band.
For increasing the capacity in the cellular network, it is generally desirable to decrease the frequency re-use factor, in particular to have a frequency re-use factor of 1. However, without the implementation of methods for suppressing the interference a reduction of the frequency re-use factor is not possible. Any wireless communication terminal should therefore be enabled to efficiently suppress interference signals from neighbouring terminal stations.